Many recording devices for audio and video include two or more microphones for recording sound from different directions. With recorded audio from different directions, one can reproduce sound on specific channels in common surround-sound channel formats. In this manner, the audio recorded may be played back to simulate the original conditions in which a person perceives the sound. For example, a typical surround-sound recording camera may include one or more microphones suited to record sound from specific directions. Thus, one example of an application specific recording device may include five directional microphones (often called cardioid or hypercardioid) pointed in five different direction (from the perspective of the camera) to record audio to be played back on a common 5.1 surround sound arrangement (i.e., a center channel, left/right channels and left/right rear channels corresponding to the “5” and a low-frequency omnidirectional signal corresponding to the “0.1”). That is, the recording camera may include directional microphones to record sound from a center channel direction (e.g., the center channel microphone is pointed straight on at 0°s), a right channel direction (e.g., slightly right on at 30°s (with respect to a point source facing the center channel at 0°s)) a left channel direction (e.g., slightly left at 330°s), a right rear channel (e.g., at 110°s) and a left rear channel (e.g., at 250°s).
With recording audio as audio signals using directional microphones at the camera location, each audio recording may be played back on a speaker corresponding to the recorded direction wherein playback speakers (i.e., channels) are similarly arranged. As a result, a person watching playback at the simulated position of the camera will hear sound as it was recorded by each directional microphone as it is now played back through a respective speaker in a respective position.
However, as recording devices become smaller and compact, the luxury of using five or more separate directional microphones for recording audio may no longer be feasible given size and processing restraints. Additionally, because of the desire to have flexibility in audio playback across different channel formats, industry standards have developed for recording audio in specific audio formats that may be later manipulated to produce audio signals that simulate the position of a microphone. Thus, even if during original audio recording, there is no specific directional microphone pointed in a left rear direction, a weighted combination of other audio signals may produce a resultant audio signal that simulates an audio signal as if it were recorded by a directional microphone pointed in the left rear direction.
With industry standards in audio recording, such as A-format/B-format and matrix format, versatile recording devices may only include two to three microphones for recording audio, but through intensive calculations of the recorded audio signals, may produce audio signals for common surround channel playback (e.g., 5.1 surround). However, the intensive calculations are cumbersome and time-consuming, so smaller devices have difficulty with the processing power needed to handle such calculations. Further, because the weighted combinations of the original signals may necessarily include crosstalk between recording microphones, the resultant audio signals tend blend together so much that the directivity that true directional microphones can record is not simulated as well.